A VIBRATIONAL STUDY OF ETHANOL ADSORPTION ON SI(100)

The adsorption of ethanol-d(0), -d(3), and -d(6) on Si(100) has been s tudied in the mid- to far-infrared region using surface infrared absor ption spectroscopy. The acquisition of infrared spectra in this freque ncy range ( < 1450 cm(-1)) is made possible by using specially prepare d Si(100) wafers which have a buried metallic CoSi2 layer that acts as an internal mirror. We find that ethanol dissociatively adsorbs acros s the Si(100) dimers near room temperature to form surface bound hydro gen and ethoxy groups. Furthermore, the ethoxy groups are oriented suc h that the C-3 upsilon axis of the methyl group is nearly perpendicula r to the surface, unlike the case for ethoxy groups bound to metal sur faces. This adsorption geometry is deduced on the basis of the surface dipole selection rule, which applies to these Si(100) samples with a buried CoSi2 layer. Ab initio cluster calculations using gradient-corr ected density functional methods confirm the proposed adsorption geome try for ethoxy on Si(100) and accurately reproduce the observed normal mode frequencies; (C) 1997 American Institute of Physics.